Once upon a time, using PPC to promote affiliate sales offered very large margins. Because of the steady increase in popularity of PPC, cost per click rates have risen across the board.
What this means for affiliate marketers, who are typically receiving small margins on products that are available from multiple sources, is that returns on PPC are often in negative territory.
Of course there are exceptions, most notably:
A] you are very astute and experienced at PPC advertising, understand advanced analytic and testing concepts to enable you to efficiently discover and exploit niches.
B] as well as being PPC-savvy as described above, you are able to spend large amounts of money to roll out on profitable PPC strategies that you have discovered from testing ads and campaigns.
For the majority of online affiliate marketers, the most efficient route is via natural search and social media, the central plank being the creation of relevant, targeted, unique content.
As an example, we write news and articles for have a couple of profitable online dating agency clients who are really effective at propagating the content we write for them - it gets into Google, they use it in email newsletters and it forms part of what they send into and talk about in their Facebook and Twitter accounts.